JP5465478B2 - Negative electrode for alkaline storage battery, alkaline storage battery, and method for producing alkaline storage battery - Google Patents

Description

The present invention relates to an alkaline storage battery negative electrode using a hydrogen storage alloy, an alkaline storage battery using the alkaline storage battery negative electrode, and a method for producing the alkaline storage battery, and particularly to the alkaline storage battery negative electrode other than the CaCu ₅ type. In the case of using a hydrogen storage alloy having a crystal structure, this hydrogen storage alloy is improved, and the output characteristics and the charge / discharge cycle characteristics under a low temperature environment are sufficiently improved.

  Conventionally, nickel-cadmium storage batteries have been widely used as alkaline storage batteries, but in recent years they have a higher capacity than nickel-cadmium storage batteries and are superior in environmental safety because they do not use cadmium. Therefore, nickel-hydrogen storage batteries using a hydrogen storage alloy for the negative electrode have come to attract attention.

  In recent years, alkaline storage batteries composed of such nickel-hydrogen storage batteries have come to be used in various portable devices, hybrid electric vehicles, and the like. It is expected to further improve the characteristics.

Here, in such an alkaline storage battery, as a hydrogen storage alloy used for the negative electrode, a rare earth-nickel-based hydrogen storage alloy having a CaCu ₅ type lattice crystal as a main phase, or a Laves type AB ₂ lattice crystal is used. A hydrogen storage alloy or the like as a main phase is generally used.

  However, hydrogen storage alloys such as those described above do not necessarily have sufficient hydrogen storage capacity, and it is difficult to increase the capacity of alkaline storage batteries, and sufficient output characteristics and charge / discharge can be achieved under low temperature conditions. There was a problem that cycle characteristics could not be obtained.

Conventionally, as shown in Patent Documents 1 and 2, etc., rare earth-Mg—Ni-based hydrogen having a crystal structure other than CaCu ₅ type in which Mg or the like is contained in the rare earth-nickel-based hydrogen storage alloy described above. It has been proposed to use a storage alloy and to increase the amount of Ni in the vicinity of the surface of the hydrogen storage alloy more than the bulk phase inside the hydrogen storage alloy.

Here, the rare earth-Mg-Ni-based hydrogen storage alloy as described above has a higher hydrogen storage capacity than the rare-earth-nickel-based hydrogen storage alloy whose main phase is the crystal of the CaCu ₅ type lattice, and generally has cracks. Since a new surface with high reactivity contributes to the discharge reaction, the discharge characteristics at low temperatures and the discharge capacity at high rate discharge were relatively good.

  Conventionally, as shown in Patent Document 3, a surface layer containing more Ni than the bulk phase inside the hydrogen storage alloy is provided on the surface of the hydrogen storage alloy, and the particle size of Ni particles in the surface layer Has been proposed to improve the low-temperature discharge characteristics and high-rate discharge characteristics in alkaline storage batteries.

  However, as described above, even when the amount of Ni in the alloy surface layer is increased or a hydrogen storage alloy in which the particle size of Ni particles in the alloy surface layer is controlled is used, the output characteristics under low temperature conditions are still The charge / discharge cycle characteristics cannot be sufficiently improved, and it has been difficult to suitably use the battery as a power source for a hybrid electric vehicle or a power tool that is required to be used in an extremely low temperature environment.

JP 2000-80429 A JP 2002-69554 A JP 2007-87886 A

This invention makes it a subject to solve the above problems in an alkaline storage battery. In the case where a hydrogen storage alloy having a crystal structure other than CaCu ₅ type is used for the negative electrode of an alkaline storage battery, this hydrogen is used. An object of the present invention is to provide an alkaline storage battery that can be suitably used as a power source for hybrid electric vehicles, electric tools, etc. by improving the storage alloy, sufficiently improving the output characteristics and charge / discharge cycle characteristics in a low temperature environment It is.

In the negative electrode for alkaline storage batteries of the present invention, in order to solve the above-described problems, the general formula Ln _1-x Mg _x Ni _yab Al _a M _b (where Ln is a rare earth element including Y, Zr, Ti At least one element selected from: M is at least one selected from V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, and B It is a seed element and satisfies the following conditions: 0.05 ≦ x ≦ 0.30, 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.50, 2.8 ≦ y ≦ 3.9. In the negative electrode for an alkaline storage battery using the hydrogen storage alloy shown, three layers of the first layer to the third layer are laminated on the surface of the bulk phase of the hydrogen storage alloy, and the first layer close to the bulk phase is The amount of oxygen contained in the alkaline solution is larger than that in the second layer located on the first layer. The second layer containing 10 atomic% or more of a soluble element and located on the first layer has a higher Ni content than the bulk phase and is located on the second layer. The third layer has a higher NiO content than the NiO content in the second layer.

  Here, in the alkaline storage battery negative electrode, it is preferable that NiO and metal Ni exist in the third layer. Thus, if NiO is present in addition to metal Ni, bonding of metal Ni to each other is suppressed, and a reduction in the reaction area of metal Ni that acts as a catalyst for charge / discharge reaction is prevented.

  If the amount of NiO in the third layer is small, it becomes impossible to sufficiently suppress the bonding of metal Ni to each other. Therefore, the ratio of the amount of Ni in NiO to the total amount of Ni of NiO and metal Ni is set as follows. It is preferably 20% or more, more preferably 40% or more. On the other hand, if the amount of NiO in the third layer is too large, the amount of metal Ni that acts as a catalyst for the charge / discharge reaction decreases, so the ratio of the amount of Ni in NiO to the total amount of Ni of NiO and metal Ni is It is preferable to make it 99% or less.

  Further, in the third layer, if a large amount of elements other than the NiO and the metal Ni is included, the charge / discharge reaction may be lowered. Therefore, the total amount of oxygen and Ni in the third layer is 90. It is preferably at least atomic percent.

  Further, if the layer thickness of the third layer is thin, the bulk phase of the hydrogen storage alloy cannot be sufficiently prevented from being corroded by the alkaline electrolyte, while the layer thickness of the third layer becomes too thick. Since the discharge performance near normal temperature is reduced, the thickness of the third layer is preferably 10 nm or more and 100 nm or less, and more preferably 40 nm or more and 70 nm or less.

  Moreover, since the reaction area which acts as a catalyst for the charge / discharge reaction decreases when the particle size of the crystal particles present in the third layer is large, the particle size of the crystal particles is preferably 7 nm or less, More preferably, it is 5 nm or less. However, if the particle size of the crystal particles present in the third layer becomes too small, the catalytic action for the charge / discharge reaction is lowered, and therefore it is preferable to use a crystal particle having a particle size of 2 nm or more.

  On the other hand, if the particle size of the crystal particles existing in the second layer is small, the movement of charges is not smoothly performed. Therefore, the particle size of the crystal particles existing in the second layer is reduced in the third layer. It is preferably larger than the particle size of the existing crystal particles, and preferably includes particles having a particle size of 10 nm or more. However, even in the crystal particles existing in the second layer, if the particle size becomes too large, the reaction area acting as a catalyst for the charge / discharge reaction is reduced, and the movement of protons is restricted and the reactivity is lowered. Therefore, it is preferable to use a crystal particle having a particle size of 50 nm or less.

  The elements soluble in the alkaline solution contained in the first layer include Ln, Al, and Mg represented by the above general formula, and such elements soluble in the alkaline solution are as described above. When the content of the first layer is 10 atomic% or more, the first layer is corroded by the alkaline electrolyte, but the bulk layer located below the first layer is prevented from being corroded by the alkaline electrolyte. Become. In particular, the presence of the third layer as described above prevents the first layer from being corroded by the alkaline electrolyte, and further suppresses the bulk phase from being corroded by the alkaline electrolyte. Durability is greatly improved.

  In addition, when using said hydrogen storage alloy for a negative electrode, since the surface area which is rich in reactivity will become small if the particle size of a hydrogen storage alloy becomes large, it is preferable to use a thing with a volume average particle diameter of 70 micrometers or less.

  And in the alkaline storage battery in this invention, the negative electrode for alkaline storage batteries which used the above hydrogen storage alloys for the negative electrode was used.

Here, in obtaining a negative electrode for an alkaline storage battery using the above hydrogen storage alloy, the hydrogen storage alloy represented by the above general formula Ln _1-x Mg _x Ni _yab Al _a M _b is oxidized, After forming the oxide layer containing NiO on the surface of the hydrogen storage alloy, the hydrogen storage alloy can be charged and discharged to form the first layer to the third layer on the surface of the hydrogen storage alloy. .

  In order to efficiently produce the alkaline storage battery as described above, the negative electrode using the hydrogen storage alloy in which the oxide layer containing NiO is formed on the surface as described above is charged and discharged in the alkaline storage battery, It is preferable to form the first to third layers on the surface of the hydrogen storage alloy.

Also, a hydrogen storage alloy represented as above by the general formula _{Ln 1-x Mg x Ni yab} Al a M b by oxidizing, in forming the oxide layer containing NiO on the surface of the hydrogen-absorbing alloy The hydrogen storage alloy may be oxidized by heat treatment in an atmosphere containing oxygen.

  Here, when the hydrogen storage alloy is oxidized by heat treatment in an atmosphere where oxygen is present as described above, the oxygen storage alloy can be appropriately oxidized if the oxygen concentration in the atmosphere or the temperature of the heat treatment is low. Since it becomes difficult, heat treatment is preferably performed at a temperature of 150 ° C. or higher in an atmosphere having an oxygen concentration of 1% or higher. However, if the temperature for the heat treatment becomes too high, the surface of the hydrogen storage alloy is oxidized more than necessary, so the temperature for the heat treatment is preferably 300 ° C. or lower.

In the alkaline storage battery of the present invention, as the hydrogen storage alloy in its negative electrode, the above-mentioned general formula _{Ln 1-x Mg x Ni yab} Al a M b surface of the bulk phase of the hydrogen-absorbing alloy represented by, the above-mentioned 1 When a layer in which three layers of the third layer to the third layer are stacked is used, in the third layer located on the outermost surface of the hydrogen storage alloy, NiO is present, so that the metal Ni bonds to each other. As a result, the reaction area of the metal Ni that acts as a catalyst for the charge / discharge reaction is increased, and the second layer located under this third layer allows the charge to move smoothly, and at low temperatures. The charge / discharge reaction is performed smoothly.

  Moreover, the bulk layer of the hydrogen storage alloy is formed by the third layer located on the outermost surface of the hydrogen storage alloy and the first layer containing 10 atomic% or more of an element soluble in the alkaline solution located on the bulk phase. Corrosion by the alkaline electrolyte is suppressed, and deterioration of the hydrogen storage alloy due to charge / discharge is prevented.

  As a result, the alkaline storage battery of the present invention has sufficiently improved output characteristics and charge / discharge cycle characteristics in a low-temperature environment, and can be suitably used as a power source for hybrid electric vehicles, electric tools, and the like.

It is a schematic sectional drawing of the alkaline storage battery produced in Example 1, Comparative example 1, and Comparative example 2 of this invention. 2 is a diagram showing a cross-sectional state of a hydrogen storage alloy in the alkaline storage battery of Example 1. FIG. 6 is a view showing a cross-sectional state of a hydrogen storage alloy in an alkaline storage battery of Comparative Example 1. FIG. It is the figure which showed the cross-sectional state of the hydrogen storage alloy in the alkaline storage battery of the comparative example 2. It is a schematic explanatory drawing of the test cell produced in Examples 1a-4a and Comparative Example 1a of this invention.

  Hereinafter, the negative electrode for an alkaline storage battery according to an embodiment of the present invention, an alkaline storage battery using the negative electrode for an alkaline storage battery, and a method for producing the same will be described, a comparative example will be given, and the negative electrode for an alkaline storage battery according to an embodiment of the present invention will be described. In the used alkaline storage battery, it is clarified that the output characteristics and charge / discharge cycle characteristics under a low temperature environment are sufficiently improved. In addition, the negative electrode for alkaline storage batteries and alkaline storage battery in this invention are not limited to what was shown to the following Example, In the range which does not change the summary, it can implement suitably.

Example 1
In Example 1, when producing an alkaline storage battery, a negative electrode and a positive electrode produced as described below were used.

[Production of negative electrode]
In preparing the negative electrode, La, Sm, Mg, Ni, and Al are mixed so as to have a predetermined alloy composition, the mixture is melted in a high-frequency induction melting furnace, and then cooled to obtain a hydrogen storage alloy. Got the ingot.

The ingot was heat-treated and homogenized, and then pulverized in an inert atmosphere and classified to obtain a hydrogen storage alloy powder having an average particle diameter corresponding to 50% by mass integral of 20 μm. In addition, as a result of analyzing the composition of this hydrogen storage alloy by high frequency plasma spectroscopy (ICP), the composition was La _0.60 Sm _0.30 Mg _0.10 Ni _3.70 Al _0.10 .

  Subsequently, the hydrogen storage alloy powder is heated in an air atmosphere at a temperature of 150 ° C. for 2 hours, and further heated in an air atmosphere at a temperature of 200 ° C. for 1 hour to form NiO on the surface of the hydrogen storage alloy. A containing oxide layer was formed. Note that the thickness of the oxide layer containing NiO formed on the surface of the hydrogen storage alloy was about 50 nm.

  Then, with respect to 100 parts by mass of the hydrogen storage alloy powder, 0.5 part by mass of a styrene / butadiene copolymer rubber (SBR) as a binder and water are added, and these are kneaded to prepare a negative electrode mixture slurry. Obtained.

Next, this negative electrode mixture slurry was uniformly applied to both surfaces of a conductive core made of punching metal, dried and pressed, and then cut into predetermined dimensions to produce a negative electrode. The filling density of the negative electrode mixture in this negative electrode was 5.0 g / cm ³ .

[Production of positive electrode]
In producing the positive electrode, a nitrate having a specific gravity of 1.75, in which a porous nickel sintered substrate having a porosity of about 85% is mixed with nickel nitrate and cobalt nitrate so that the atomic ratio of nickel to cobalt is 10: 1. After immersing in the solution to hold the nickel salt and cobalt salt in the pores of the porous nickel sintered substrate, the porous nickel sintered substrate is immersed in a 25% by mass aqueous sodium hydroxide solution. The nickel salt and cobalt salt were converted into nickel hydroxide and cobalt hydroxide, respectively, and nickel hydroxide and cobalt hydroxide were retained in the pores. Subsequently, the porous nickel sintered substrate in which the nickel hydroxide and the cobalt hydroxide were held in the holes as described above was sufficiently washed with water to remove the alkaline solution and dried.

  Then, after immersing the porous nickel sintered substrate in which the nickel hydroxide and the cobalt hydroxide are held in the holes in the above-described nitrate solution, the porous nickel-sintered substrate is immersed in the aqueous sodium hydroxide solution. The filling process of washing and drying was repeated 6 times, and the positive electrode active material nickel hydroxide was filled into the pores of the porous nickel sintered substrate.

And after drying the porous nickel sintered board which filled the positive electrode active material which consists of nickel hydroxide in the hole in this way at room temperature, it cut | disconnected to the predetermined dimension and produced the positive electrode. The packing density of the positive electrode active material in this positive electrode was 2.5 g / cm ³ .

  Then, a polypropylene non-woven fabric was used as the separator, and a 30% by mass potassium hydroxide aqueous solution was used as the alkaline electrolyte. A cylindrical storage battery having a design capacity of 6000 mAh as shown in FIG. 1 was produced.

  Here, in producing the alkaline storage battery, as shown in FIG. 1, the separator 3 is interposed between the positive electrode 1 and the negative electrode 2, and these are wound in a spiral shape in the battery can 4. The positive electrode 1 is connected to the positive electrode lid 6 via the positive electrode lead 5 and the negative electrode 2 is connected to the battery can 4 via the negative electrode lead 7, and the alkaline electrolyte is poured into the battery can 4. After letting it liquid, the battery can 4 and the positive electrode lid 6 were sealed with an insulating packing 8 therebetween, and the battery can 4 and the positive electrode lid 6 were electrically separated by the insulating packing 8. Further, a closing plate 11 urged by a coil spring 10 is provided between the positive electrode cover 6 and the positive electrode external terminal 9 so as to close the gas discharge port 6a provided in the positive electrode cover 6, and the battery When the internal pressure of the battery rose abnormally, the coil spring 10 was compressed so that the gas inside the battery was released into the atmosphere through the vent hole formed in the positive electrode external terminal 9. The amount of alkaline electrolyte was 2.5 g per battery capacity 1 Ah.

  Next, the alkaline storage battery thus produced was charged in a temperature atmosphere of 25 ° C. at a current of 6000 mA for 1 hour and 12 minutes, rested for 1 hour, and then allowed to stand in a temperature atmosphere of 70 ° C. for 24 hours. In an atmosphere of 45 ° C., the battery was discharged at a current of 6000 mA until the battery voltage became 0.3 V, and this was used as one cycle for two cycles of charge / discharge to activate, thereby obtaining an alkaline storage battery of Example 1. .

(Comparative Example 1)
In Comparative Example 1, in the production of the negative electrode in Example 1 above, the above-mentioned hydrogen storage alloy powder was not heat-treated, and an oxide layer containing NiO was not formed on the surface of the hydrogen storage alloy. In the same manner as in Example 1 above, an alkaline storage battery was produced, and the alkaline storage battery thus produced was activated by charging and discharging in the same manner as in the alkaline storage battery in Example 1 above. A storage battery was obtained.

(Comparative Example 2)
In Comparative Example 2, an alkaline storage battery was produced using a negative electrode produced by acid treatment of a hydrogen storage alloy powder using a hydrochloric acid solution. Specifically, as shown in the following paragraphs 0045 to 0052, an alkaline storage battery of Comparative Example 2 was produced.

[Preparation of negative electrode]
In producing the negative electrode, the rare earth elements La, Pr, and Nd, Zr, Mg, Ni, and Al are mixed so as to have a predetermined alloy composition, and the mixture is melted in a high frequency induction melting furnace. Thereafter, this was cooled to obtain a hydrogen storage alloy ingot.

Then, the hydrogen storage alloy ingot is heat treated and homogenized, and then the hydrogen storage alloy ingot is pulverized in an inert atmosphere and classified to obtain a hydrogen storage alloy having a volume average particle size of 30 μm. An alloy powder was obtained. As a result of analyzing the composition of the hydrogen storage alloy by high frequency plasma spectroscopy (ICP), the composition of the hydrogen storage alloy was (La _0.20 Pr _0.39 Nd _0.40 Zr _0.01 ) _0.84 Mg _0.16 Ni _3.15 Al _0.20 . .

  Next, 2.0 kg of the hydrogen storage alloy powder obtained as described above was immersed in 2 liters of hydrochloric acid solution (pH 1) and subjected to acid treatment for about 6 minutes until pH 7 was reached. An alloy powder was obtained.

  Then, 0.5 parts by weight of polyethylene oxide as a binder and 0.6 parts by weight of polyvinyl pyrrolidone are added to 100 parts by weight of the acid-treated hydrogen storage alloy powder as described above. A mixture slurry was obtained.

And this negative mix slurry was apply | coated uniformly on both surfaces of the electroconductive core which consists of punching metals, and after drying and pressing this, it cut | disconnected to the predetermined dimension and produced the negative electrode. The filling density of the negative electrode mixture in this negative electrode was 5.0 g / cm ³ .

[Preparation of positive electrode]
In preparing the positive electrode, 50 parts by weight of a 0.2% by weight hydroxypropylcellulose aqueous solution was added to 100 parts by weight of nickel hydroxide as the positive electrode active material, and these were mixed to prepare a positive electrode slurry. Then, this positive electrode slurry was filled in a nickel foam, dried and rolled, and then cut into a predetermined size to produce a positive electrode composed of a non-sintered nickel electrode. The packing density of the positive electrode active material in this positive electrode was 2.5 g / cm ³ .

Further, as the alkaline electrolyte, an alkaline aqueous solution containing KOH, NaOH, and LiOH.H ₂ O at a weight ratio of 8: 0.5: 1 and the sum of which is 30% by weight is used. A cylindrical storage battery having a design capacity of 3000 mAh as shown in FIG.

  Next, the alkaline storage battery produced as described above was charged at a current of 300 mA for 16 hours under a temperature condition of 25 ° C., and then discharged at a current of 600 mA until the battery voltage reached 1.0 V. The battery was charged for 16 hours at a current of 300 mA, and then discharged at a current of 3000 mA until the battery voltage reached 1.0 V. Furthermore, after the battery voltage reaches the maximum value at a current of 3000 mA, the alkaline storage battery is charged until it decreases by 10 mV, left for 0.5 hours, and then the battery voltage reaches 1.0 V at a current of 9000 mA. The battery was discharged and activated by performing 3 cycles to obtain an alkaline storage battery of Comparative Example 2.

  Then, the alkaline storage batteries of Example 1, Comparative Example 1 and Comparative Example 2 activated by charging and discharging in this manner are disassembled, the hydrogen storage alloy in each negative electrode is taken out, and the taken out hydrogen storage alloys are cleaned. After removing the alkaline electrolyte and the binder and drying them, a cross-sectional sample of each hydrogen storage alloy was prepared, and the cross-sectional structure of each hydrogen storage alloy was measured with a transmission electron microscope TEM (manufactured by JEOL: JEM). -2010F type), the state of the hydrogen storage alloy in the alkaline storage battery of Example 1 is shown in FIG. 2, the state of the hydrogen storage alloy in the alkaline storage battery of Comparative Example 1 is shown in FIG. The state of the hydrogen storage alloy in the alkaline storage battery 2 is shown in FIG.

  As a result, in the hydrogen storage alloy in the alkaline storage battery of Example 1, as shown in FIG. 2, on the bulk phase B, the first layer S1 having a layer thickness of 20 to 40 nm in which crystal particles cannot be confirmed. And a third layer S2 having a crystal grain size of about 10 nm and a layer thickness of 80 to 150 nm, and a third layer S3 having a crystal grain size of about 5 nm and a layer thickness of about 50 nm. It was.

  On the other hand, in the hydrogen storage alloy in the alkaline storage battery of Comparative Example 1, as shown in FIG. 3, on the bulk phase B, the first layer S1 having a layer thickness of 20 to 40 nm in which crystal particles cannot be confirmed; The second layer S2 having a crystal grain size of about 10 nm and a layer thickness of 80 to 150 nm was simply laminated.

  Moreover, in the hydrogen storage alloy in the alkaline storage battery of Comparative Example 2, as shown in FIG. 4, on the bulk phase B, the first layer S1 having a layer thickness of 20 to 50 nm in which crystal particles cannot be confirmed; The two layers of the second layer S2 having a crystal grain size of 10 to 15 nm and a layer thickness of 50 to 80 nm were simply stacked.

  In each of the above hydrogen storage alloys, the boundary between the first layer and the second layer is not clear, and the crystal grain size gradually increases from the first layer toward the second layer. The portion that could not be determined was the first layer, and the portion that could be clearly determined was the second layer.

  Moreover, about the hydrogen storage alloy in the alkaline storage battery of Example 1 above, the ratio of the constituent elements in the bulk phase and the first to third layers described above was determined using a TEM-EDS measuring device (NORAN, UTW Si (Li ) For the second layer and the third layer, the ratio of the Ni amount in NiO to the total Ni amount of NiO and metal Ni is determined for the second and third layers, and the result is The results are shown in Table 1 below. Specifically, the above ratios in each layer were calculated on the assumption that all metal elements other than rare earth and Ni form oxides with oxygen in the layers, and all the remaining oxygen forms NiO.

  As a result, in the hydrogen storage alloy in the alkaline storage battery of Example 1, there is almost no metal component other than Ni in the second layer and the third layer, and the first layer is a rare earth element soluble in an alkaline solution, Al. Mg was close to the bulk phase of the alloy. Further, the amount of oxygen in the first layer to the third layer is large in the first layer and the third layer, and is small in the second layer located in the middle. The amount of oxygen in the first layer with respect to the second layer is about It was 1.5 times.

  Electron diffraction revealed that mainly the metal Ni was present in the second layer and the NiO was mainly present in the third layer. The ratio of the Ni amount in NiO to the total Ni amount of NiO and metal Ni in the second layer was 13.9%, whereas the ratio in the third layer was 52.1%. The NiO content in the third layer was higher than the NiO content in the second layer.

  Moreover, also about the comparative example 1 and the comparative example 2, when the ratio of a structural element was calculated | required using said TEM-EDS measuring apparatus, about the hydrogen storage alloy in the alkaline storage battery of the comparative example 1, the 1st layer is an alloy. In the state close to the bulk phase, the second layer had reduced metal elements other than rare earth and Ni. Moreover, about the hydrogen storage alloy in the alkaline storage battery of Comparative Example 2, the first layer is in a state close to the bulk phase of the alloy, and the second layer has a metal element other than rare earth and Ni, which is smaller than that in Comparative Example 1. It was. Moreover, it turned out that Ni in the 2nd layer of the comparative example 1 and the comparative example 2 exists mainly as metal Ni from the electron beam diffraction.

  Next, the alkaline storage batteries of Example 1 and Comparative Example 1 that were activated by charging and discharging as described above were charged with a charging current of 6000 mA for 30 minutes in a temperature atmosphere of 25 ° C., respectively, and rested for 1 hour. I let you.

  Thereafter, each of the alkaline storage batteries described above was charged for 20 seconds at a current of 1800 mA in a temperature atmosphere of −30 ° C., paused for 30 minutes, discharged for 10 seconds at a current of 4200 mA, paused for 30 minutes, and then Charge for 20 seconds at a current of 4200 mA, pause for 30 minutes, then discharge for 10 seconds at a current of 7800 mA, pause for 30 minutes, then charge for 20 seconds at a current of 6000 mA, pause for 30 minutes, and then at a current of 12000 mA Discharge for 10 seconds, pause for 30 minutes, then charge for 20 seconds at a current of 7800 mA, pause for 30 minutes, then discharge for 10 seconds at a current of 16200 mA, pause for 30 minutes, then charge for 20 seconds at a current of 10200 mA After 30 minutes of rest, the battery was discharged at a current of 19800 mA for 10 seconds. In the battery voltage at 10 seconds after discharged was measured and plotted with each discharge current and the battery voltage to determine the above-mentioned discharge the I-V characteristic of the alkaline storage batteries in the ambient temperature range from -30 ° C..

  And based on said discharge IV characteristic, the discharge current at the time of 0.9V of each alkaline storage battery in a temperature atmosphere of −30 ° C. is obtained, and the low temperature discharge output of each alkaline storage battery at a low temperature of −30 ° C. is obtained. The low temperature discharge output in the alkaline storage battery of Example 1 was calculated using the low temperature discharge output in the alkaline storage battery of Comparative Example 1 as the low temperature discharge output characteristic 100, and the results are shown in Table 2 below.

  In addition, each of the alkaline storage batteries of Example 1 and Comparative Example 1 activated by charging and discharging as described above was charged with a charging current of 6000 mA for 30 minutes in a temperature atmosphere of 25 ° C. and rested for 1 hour. It was.

  Thereafter, each alkaline storage battery described above was charged at a current of 2400 mA for 20 seconds in a temperature atmosphere of 25 ° C., rested for 30 minutes, discharged for 10 seconds at a current of 10200 mA, rested for 30 minutes, and then 10200 mA. The battery was charged for 20 seconds, and rested for 30 minutes, then discharged for 10 seconds at a current of 19800 mA, rested for 30 minutes, then charged for 20 seconds at a current of 15000 mA, rested for 30 minutes, and then 10 seconds at a current of 30000 mA. Discharged for 30 seconds, paused for 30 minutes, then charged for 20 seconds at a current of 19800 mA, paused for 30 minutes, discharged for 10 seconds at a current of 40200 mA, paused for 30 minutes, and then charged for 20 seconds at a current of 25200 mA , After resting for 30 minutes, discharged at 49800 mA for 10 seconds, The battery voltage at 10 seconds after discharged at a discharge current is measured and plotted with each discharge current and the battery voltage to determine the above-mentioned discharge the I-V characteristic of the alkaline storage batteries in the ambient temperature range from 25 ° C..

  And based on said discharge IV characteristic, the discharge current at the time of 0.9V of each alkaline storage battery in a 25 degreeC temperature atmosphere was calculated | required, and discharge output IPx in 25 degreeC of each alkaline storage battery was computed.

  Next, each alkaline storage battery after measuring IPx of Example 1 and Comparative Example 1 was charged in a temperature atmosphere of 25 ° C. for 30 minutes at a charging current of 6000 mA, and then in a temperature atmosphere of 45 ° C. , Intermittent charging / discharging was repeated 18000 cycles at a current of 50 A while controlling the depth of charge (SOC) to be maintained within the range of 40 to 60%.

  And using each alkaline storage battery after repeating 18000 cycles of intermittent charging / discharging in this way, in the same manner as in the above case, the IV characteristics in each alkaline storage battery in a temperature atmosphere at 25 ° C. were obtained, The discharge output IPy at 25 ° C. of the alkaline storage battery is calculated, the output deterioration rate after 18000 cycles is obtained by the following formula, the output deterioration rate in the alkaline storage battery of Comparative Example 1 is set as the output deterioration 100, and the alkaline storage battery of Example 1 The output deterioration was calculated and the results are shown in Table 2 below.

  Output deterioration rate after 18000 cycles = (IPx−IPy) / IPx

  As a result, the alkaline storage battery of Example 1 using the hydrogen storage alloy in which the three layers of the first layer to the third layer as described above were formed on the bulk phase had the first layer on the bulk phase. Compared with the alkaline storage battery of Comparative Example 1 using a hydrogen storage alloy in which two layers consisting of the second layer are formed, the low-temperature discharge output characteristics are greatly improved and the output deterioration is greatly reduced, which is excellent. Output life characteristics were obtained.

Example 1a
In Example 1a, in preparing the hydrogen storage alloy electrode used for the negative electrode, a hydrogen storage alloy powder having a composition of La _0.60 Sm _0.30 Mg _0.10 Ni _3.70 Al _0.10 was prepared in the same manner as in Example 1 above. After heating in an air atmosphere at a temperature of 150 ° C. for 2 hours, and further heat-treating in an air atmosphere at a temperature of 200 ° C. for 1 hour, an oxide layer containing NiO is formed on the surface of the hydrogen storage alloy. A hydrogen storage alloy electrode having a capacity of 90 mAh was prepared by mixing nickel powder of a conductive agent at a ratio of 3 parts by mass with 1 part by mass of the hydrogen storage alloy powder, and pressing the mixture into a pellet. Produced.

The hydrogen storage alloy electrode produced as described above is used for the negative electrode, while the positive electrode uses a sintered nickel electrode formed in a cylindrical shape having an excess capacity relative to the negative electrode, and 30 for the alkaline electrolyte. Using a mass% aqueous potassium hydroxide solution, a test cell as shown in FIG. 5 was produced.

  Here, in the test cell, the alkaline electrolyte 23 is accommodated in a polypropylene container 20, and the reference electrode 24 including a negative electrode 22 and a mercury oxide electrode is provided in the cylindrical positive electrode 21. And the positive electrode 21, the negative electrode 22, and the reference electrode 24 were immersed in the alkaline electrolyte 23.

  The test cell was charged at a current of 45 mA for 170 minutes in a temperature atmosphere of 25 ° C., rested for 10 minutes, and then the potential of the negative electrode with respect to the reference electrode became −0.7 V at a current of 45 mA. The test cell was activated by discharging and resting for 20 minutes, and repeating this charge and discharge for 8 cycles.

Example 2a
In Example 2a, in the production of the hydrogen storage alloy electrode in Example 1a above, the powder of the hydrogen storage alloy having the composition La _0.60 Sm _0.30 Mg _0.10 Ni _3.70 Al _0.10 was heated in an air atmosphere at a temperature of 150 ° C. After heating for 2 hours, the heat treatment was further performed in an air atmosphere at a temperature of 200 ° C. for 0.25 hours to form an oxide layer containing NiO on the surface of the hydrogen storage alloy. A test cell was produced in the same manner as in Example 1a, and the test cell produced in this way was activated by being charged and discharged in the same manner as the test cell in Example 1a.

(Example 3a)
In Example 3a, in the production of the hydrogen storage alloy electrode in Example 1a above, the powder of the hydrogen storage alloy having the composition La _0.60 Sm _0.30 Mg _0.10 Ni _3.70 Al _0.10 was heated in an air atmosphere at a temperature of 150 ° C. After heating for 2 hours, the heat treatment was further performed in an air atmosphere at a temperature of 200 ° C. for 0.5 hours to form a hydrogen storage alloy surface on which an oxide layer containing NiO was used. A test cell was produced in the same manner as in Example 1a, and the test cell produced in this way was activated by being charged and discharged in the same manner as the test cell in Example 1a.

Example 4a
In Example 4a, in the production of the hydrogen storage alloy electrode in Example 1a above, the powder of the hydrogen storage alloy having the composition La _0.60 Sm _0.30 Mg _0.10 Ni _3.70 Al _0.10 was heated in an air atmosphere at a temperature of 150 ° C. After heating for 2 hours and further heat-treating in an air atmosphere at a temperature of 200 ° C. for 2 hours to form an oxide layer containing NiO on the surface of the hydrogen-absorbing alloy, the other examples described above are used. A test cell was produced in the same manner as 1a, and the test cell produced in this way was activated by charging and discharging in the same manner as in the test cell of Example 1a.

(Comparative Example 1a)
In Comparative Example 1a, the hydrogen storage alloy powder having the composition La _0.60 Sm _0.30 Mg _0.10 Ni _3.70 Al _0.10 in the production of the hydrogen storage alloy electrode in Example 1a described above was compared with the case of Comparative Example 1 above. Similarly, heat treatment was not performed, and an oxide layer containing NiO was not formed on the surface of the hydrogen storage alloy. Otherwise, a test cell was produced in the same manner as in Example 1a, and thus produced. The test cell was activated by charging and discharging in the same manner as the test cell of Example 1a above.

  And as mentioned above, after processing of Examples 1a to 4a and Comparative Example 1a, the cross-sectional structure of each hydrogen storage alloy is observed with a transmission electron microscope TEM (manufactured by JEOL: JEM-2010F type) as described above. As a result, in Examples 1a to 4a, as in the case after the activation of Example 1 above, a 34-68 nm layer like the third layer described above was formed on the bulk phase. On the other hand, the third layer was not present in Comparative Example 1a. Moreover, about each hydrogen storage alloy of said Example 1a-4a, the layer thickness of said 3rd layer in the outermost surface of each hydrogen storage alloy was calculated | required, and the result was shown in following Table 3.

  In addition, each of the test cells of Examples 1a to 4a and Comparative Example 1a activated as described above was charged at a charge current of 45 mA for 170 minutes in a temperature atmosphere of 25 ° C., and then rested for 10 minutes. Furthermore, it was rested in a temperature atmosphere of −20 ° C. for 4 hours, and then discharged in a temperature atmosphere of −20 ° C. with a discharge current of 45 mA until the potential of the negative electrode with respect to the reference electrode became −0.7 V, The discharge capacity at −20 ° C. in each test cell is obtained, the discharge capacity in the test cell of Comparative Example 1a is defined as the low temperature discharge characteristic 100, and the low temperature discharge characteristics in each test cell of Examples 1a to 4a are calculated. The results are shown in Table 3 below.

  As a result, each of the test cells of Examples 1a to 4a using the hydrogen storage alloy in which the three layers of the first layer to the third layer as described above were formed on the bulk phase had the first cells on the bulk phase. Compared with the test cell of Comparative Example 1a using a hydrogen storage alloy in which two layers consisting of one layer and a second layer are formed, the low-temperature discharge characteristics are high, and discharge at a low temperature of −20 ° C. The capacity was getting bigger.

  Further, as a result of comparing the test cells of Examples 1a to 4a, the layer thickness of the third layer on the outermost surface of the hydrogen storage alloy was 40 nm or more. Those of 3a and 4a have higher low-temperature discharge characteristics than those of Example 2a in which the thickness of the third layer on the outermost surface of the hydrogen storage alloy is less than 40 nm, and a low temperature of −20 ° C. The discharge capacity at the bottom was even larger.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Battery can 5 Positive electrode lead 6 Positive electrode cover 6a Gas discharge port 7 Negative electrode lead 8 Insulation packing 9 Positive electrode external terminal 10 Coil spring 11 Closure board 20 Container 21 Positive electrode 22 Negative electrode 23 Alkaline electrolyte 24 Reference electrode B Bulk Phase S1 1st layer S2 1st layer S3 3rd layer

Claims (11)

General formula Ln _1-x Mg _x Ni _yab Al _a M _b (wherein Ln is at least one element selected from rare earth elements including Y, Zr, Ti, M is V, Nb, Ta, Cr) , Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, B, and at least one element selected from 0.05 ≦ x ≦ 0.30, 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.50, 2.8 ≦ y ≦ 3.9.) in the negative electrode for an alkaline storage battery using the hydrogen storage alloy described above. Three layers of the first layer to the third layer are laminated on the surface of the bulk phase, and the first layer close to the bulk phase contains oxygen contained more than the second layer located on the first layer. The amount of the element that is soluble in the alkaline solution is 10 atomic% or more, and the second layer located on the first layer is: The Ni content is higher than the bulk phase, and the third layer located on the second layer is characterized in that the NiO content is higher than the NiO content in the second layer. Negative electrode for alkaline storage battery.   2. The negative electrode for an alkaline storage battery according to claim 1, wherein NiO and metal Ni are present in the third layer.   3. The negative electrode for an alkaline storage battery according to claim 1, wherein the ratio of the Ni content in NiO to the total Ni content of NiO and metal Ni in the third layer is 20% or more and 99% or less. A negative electrode for an alkaline storage battery.   The alkaline storage battery negative electrode according to any one of claims 1 to 3, wherein the total amount of oxygen and Ni in the elements contained in the third layer is 90 atomic% or more. Negative electrode for alkaline storage battery.   5. The negative electrode for an alkaline storage battery according to claim 1, wherein the layer thickness of the third layer is 10 nm or more and 100 nm or less.   The negative electrode for an alkaline storage battery according to any one of claims 1 to 5, wherein the crystal particle size present in the third layer is greater than the particle size of the crystal particles present in the second layer. A negative electrode for an alkaline storage battery characterized by being small.   The negative electrode for an alkaline storage battery according to any one of claims 1 to 6, wherein the crystal particles present in the third layer are composed only of crystal particles having a particle size of 7 nm or less. A negative electrode for alkaline storage batteries.   8. The negative electrode for an alkaline storage battery according to claim 1, wherein Ln, Al, and Mg represented by the above general formula are included as elements soluble in the alkaline solution in the first layer. A negative electrode for an alkaline storage battery.   In the alkaline storage battery provided with the positive electrode, the negative electrode using a hydrogen storage alloy, and alkaline electrolyte, the negative electrode for alkaline storage batteries of any one of Claims 1-8 was used as said negative electrode. An alkaline storage battery characterized by that. In manufacturing the alkaline storage battery according to claim 9, the hydrogen storage alloy represented by the general formula Ln _1-x Mg _x Ni _yab Al _a M _b is oxidized, and NiO is added to the surface of the hydrogen storage alloy. A step of forming an oxide layer including the step of charging and discharging the alkaline storage battery, and a step of forming the first to third layers on the surface of the hydrogen storage alloy on which the oxide layer including NiO is formed. The manufacturing method of the alkaline storage battery characterized by performing.   The method for producing an alkaline storage battery according to claim 10, wherein the hydrogen storage alloy is heat-treated at a temperature of 150 ° C. or higher in an oxygen-containing atmosphere when oxidizing the hydrogen storage alloy. A method for producing an alkaline storage battery.